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Rob Rob Bassman Micro Build

Discussion in 'Shock Brother's DIY Amps' started by DimensionofSound, Apr 16, 2021.

  1. DimensionofSound

    DimensionofSound TDPRI Member

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    52308B79-D7D1-4F27-BF92-769A3FFB351C.jpeg Hello,

    Planning my Bassman Micro build with EF80s using the Antek transformer. Is the attached wiring correct?

    Thanks for your help.
     
    Last edited: Apr 16, 2021
  2. DimensionofSound

    DimensionofSound TDPRI Member

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    Attached is my chassis layout. Not sure if I'm going to put the bright cap on a switch yet.
     

    Attached Files:

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  3. MatchlessMan

    MatchlessMan Tele-Holic

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    Subscribed!
     
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  4. NSB_Chris

    NSB_Chris Tele-Meister

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    Don't you want the passive effects loop after the cathode follower? The DC coupled cathode follower is the secret sauce of the preamp and it is buffered to drive the passive effects loop cable better. That also allows adding time based effects after the distortion rather than right before.
     
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  5. NSB_Chris

    NSB_Chris Tele-Meister

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    I see you went away from the Bassman tone stack filtering.

    I hesitate to mention grounding scheme as strong opinions tend to get well ... heated. If you are going to use a separate ground for the power section and the preamp section, you might want to consider splitting the ground so that the PI and presence section is grounded with the power section. Then the preamp is grounded together and the power section including the PI is grounded together. Your board is well suited for this since your B+3 filter is moved to the right with the preamp. Just a thought.
     
  6. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    It may be worth doing a Save As on a PDF to make a JPG which folks can view inline.

    Is yours (below) purely Rob's layout, or did you change something? If it is Rob’s, I suggest no one is eager to proofread the whole thing for obvious errors, tho I’m sure Rob would be the first to say nobody's perfect.

    Maybe you can tell us what you changed, or at least what parts you’re wondering about?

    4030859B-29CA-49C2-9260-6047FDE99247.jpeg
     
  7. DimensionofSound

    DimensionofSound TDPRI Member

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    It’s Rob layout. Just need someone to confirm the transformer wiring is correct since he doesn’t provide a layout for the Antek transformer.
     
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  8. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Aha, thanks, makes sense. One of the challenges of these micro amps is there are so many options, and relatively few completed builds to detail each different option.

    Hmm. Is yours the same as the Antek detail drawing on his page (below)? Were there questions about his? I'm not aware of the issues with toroidal PTs, but ask about anything you're wondering. There are toroid-smart folks here.

    upload_2021-4-16_10-46-8.jpeg
     
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  9. DimensionofSound

    DimensionofSound TDPRI Member

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    Thank you. Just double checking, being cautious since like you said there are so many options and it’s not specifically spelled out (draw on the exact layout, instead the 5E3 layout portion is used and I deleted the standby switch) for the Micro Bassman.
     
  10. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Ah, OK, good. Let's see if folks who know toroidal will chip in. I believe there are mounting questions, like mounting them 'upside down' can shorten the wire runs (but makes the labels look funny.)

    I looked into 'em for an hour or so when I was thinking about the Bassman Micro, and IIRC couldn't quite figure out mounting bolt / chassis isolation issues. But I never got very far with my plans. My theoretic interest was in having a handsome, inexpensive little amp head with all the tubes and transformers showing, and I decided a toroidal in its shrinkwrap didn't fit into my desired look, while the toroid covers made 'em about as expensive as standard PTs. And then the transformers plus a few other things made them *not inexpensive.* But I'm sure a toroidal PT could be readily used and as you know they also have advantages.
     
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  11. DimensionofSound

    DimensionofSound TDPRI Member

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    Appreciate your help.

    Sounds cool. I’m not a fan of the exposed look for guitar amps personally. Even the little cage ones. I got a nice tweed cab for my build.
     
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  12. DimensionofSound

    DimensionofSound TDPRI Member

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    This is Robs design but I’m all ears. Would you mind drawing where you would place it please?
     
  13. NSB_Chris

    NSB_Chris Tele-Meister

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    Honestly, if you really want an effects loop I would put an active rather than a passive effects loop and I would put it after the tone stack so that you shape the tone you want before sending to the time based effects. If you want gain from stomp boxes, you put them in front of the amp and put any post distortion effects in the effects loop. Most tube driven effects loop deigns that I have seen use a cathode follower to drive the send side. Otherwise you risk the in load of the effects loop dragging down the driving stage. Post FX loop, you have a regular gain stage for the recovery.

    Really depends on how you plan to use the amp and what complexity you are willing to implement. If you are going to bring the amp up to a sweet spot at the edge of breakup, then you may not need an FX loop at all and put whatever pedals you want in front of the amp. That is probably the most common application of the classic Bassman circuit.

    For placement of the passive FX loop after the cathode follower, I will defer to others that have more experience with passive FX loops.
     
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  14. DimensionofSound

    DimensionofSound TDPRI Member

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    Honestly I’ll probably never use it. I’m not really a loop guy. That’s the plan edge of breakup maybe over, something I can play at home and get some tube distortion without being crazy loud. I appreciate all your comments. Helps me learn.
     
  15. robrob

    robrob Poster Extraordinaire Ad Free Member

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    DimensionofSound, your power transformer amp looks perfect.

    I recommend you put the FX loop between the MV wiper and the following coupling cap as shown on the Bassman Micro EF80 layout. Passive won't work with every pedal but they tend to work better than expected. It's a simple add so why not.
     
    Last edited: Apr 23, 2021
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  16. DimensionofSound

    DimensionofSound TDPRI Member

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    Thank you Rob.
     
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